The effects of deforestation and biomass burning in tropical dry forests (TDF) remain a little studied phenomenon. We quantified total aboveground biomass (TAGB), carbon and nutrient (N,S,Ca,P,K) loss under two separate fire severity scenarios; one early when the fuels were higher in moisture content, one later when the slash fuels were drier and then compared the loss and the regrowth of the sites. The TAGB and nutrients were measured (1993-1995) after the forest was cut, after a forest slash fire, one year after pasture establishment and, two years after the slash fire, biomass was quantified before and after a pasture fire. The treatments were based upon time from slash to burn. The low severity fires (Baja) were burned 65 days and the higher severity fires (Alta) were burned 95 days after the initial slash of TDF on ��� 3.5 ha near the Chamela Biological Research Station on the Ejido San Mateo, Jalisco, Mexico. As a result of the 1993 slash fire, TAGB declined from 118.2 to 43.6 Mg ha����� (62%) in the Baja treatment and from 134.9 to 26.8 Mg ha����� (80%) in the Alta treatment. Nutrients pools declined 57-88% with ��� 10% higher combustion of the Alta pools. In 1995, after the pasture fires, TAGB declined from 40.3 to 14.8 Mg ha����� (63%) and from 29.0 to 7.6 Mg ha����� (75%) in the Alta treatment and nutrient pools declined 57-88%. Total aboveground biomass loss from 1993-1995 was 103.4 Mg ha����� (87%) in the Baja treatment and 127.3 Mg ha����� (94%) in the Alta treatment. Carbon and nutrient losses ranged from 87-96% over the three-year study. We found little ash retention after fire, no increase in nutrient soil concentrations and, highly volatized nutrients (i.e. Ca and P) were essentially lost due to wind and water erosion on 40 to 60% slopes. Wood decomposition between fires reduced TAGB and nutrient pools by 15% in the Baja treatment and 3% in the Alta treatment. / Graduation date: 2000

Despite the recognized role of soil arthropod fauna on nutrient cycling and decomposition processes, many aspects of the effects of sylvicultural methods in forest ecosystems upon their biology remain poorly understood. The long term effects of prescribed fires on soil arthropods in forest ecosystems in the Pacific Northwest have never been studied. Soil samples were taken from three sites located in the Willamette National Forest in 1992: paired sites that were either clear-cut without burning and clear-cut with burning 40 years ago. One hundred and eight samples were processed; the arthropods were separated, identified and counted. To study the biology and behavior of some arthropods, eight species of oribatid mites were reared in laboratory conditions. Their life cycle, feeding behavior and reproduction were studied. Results indicated that there were no statistical significant treatment differences either in terms of total numbers of organisms or biomass. However, the majority of the commonest taxa did show offsetting treatment responses. A total of 204 taxa were found in the three sites. The most important groups included Collembola, mites, and insects. Other groups also represented, but in smaller numbers, were spiders, symphylans, pseudoscorpions, and centipedes. Of all these groups, oribatid mites was the best represented and appears to be a useful indicator of disturbances. / Graduation date: 1995